Most commercially available microscopes are designed in such a way that, depending on the requirements of the preparation to be examined, different lenses can be inserted into the optical path. For this purpose, there is a thread into which different lenses can be screwed. Microscopes often comprise means in which several lenses are screwed in or stored and which allow a simple insertion of the lenses into the optical path of the microscope. Devices of this type are usually configured as lens turrets.
Microscopes with lenses that can be screwed out and that are fitted with a laser such as, for instance, laser scanning microscopes or microscopes with a laser device for specimen manipulation entail the disadvantage that hazardous laser radiation might escape in an undesired and uncontrolled manner if the lens is inadvertently removed.
Microscopes with interchangeable lenses also have the drawback that the relatively small, although usually expensive, lenses can be easily removed or can be easily lost. This aspect is of particular relevance in the case of microscopes employed in schools.
Japanese patent JP 2000221408 A2 discloses a lens turret with a cylindrical protective ring that is affixed with screws and that encompasses all lenses, thus making unauthorized removal more difficult. The protective ring, however, greatly limits the space around the lenses, which has a very detrimental impact when it comes to bringing laboratory devices such as, for example, manipulators or micropipettes, close to the specimen. Besides, authorized replacement of the lenses can only be carried out with considerable effort, namely, by dismantling the specimen stage or the microscope stand.